Upgrade pip in the venv when we build it.
Upgrade pip in the venv when we build it.

Change-Id: I924975170c9e3a1ef23b5195cb3a6eed675ec043

hyakuhei/cleantox,openstack-dev/hacking,hyakuhei/cleantox,emonty/oslo-hacking,zancas/hacking,zancas/hacking,openstack-dev/hacking,emonty/oslo-hacking